Well that's the point, isn't it? Exaggerated to where it just looks stupid because no one acts that way. I'm sorry, they don't. It clearly looks to me like they were trying to copy what they think the littlest kids would be saying; or copying how kids in toy commercials give overblown reactions to what's being advertised.
I really don't know how you can't see this.
I know for a fact that people (rational sensible-minded adults), act that way. I've worked in places where it happens, albeit slightly exaggerated because they do it without the hand gestures (they use totally different stupid friendly inside jokes instead).
Heck, offices throw less subtle celebrations for less consequential things (like a person getting his first commendation from a customer). Or Halloween.
EDIT: And just in case, yes, they were a "mirror image" of that scene. There's that attractive officemate who likes giving worthless exclamations, that slightly older man who will make the so-unfunny-it's-funny joke, that young man who will think hard for a comment, make it, then go silent, that boss who would try to pump up people for worthless celebrating, that really silent good performer who will express appreciation, and that man who will try to flirt with everyone wearing a skirt.
Like I said, this is an utterly senseless nitpick that I cannot see the rationale behind. So you haven't seen people do it. Meet more people, I guess?